Active implantable medical devices utilize sensors for collecting the signals and controlling various functions. Some sensors can notably be integrated with a lead, which is itself connected to the case of a pulse generator. Typical examples of such sensors are blood pressure sensors or endocardial acceleration (EA) sensors mounted level with the distal tip of an endocardial lead that is introduced in the myocardium, and connected to the case of a pacemaker of defibrillator.
The present invention more particularly relates to a biocompatible component that is implantable in the human body, and embedding an active element that is hermetically encapsulated. The active element may be a sensor for the measurement of a physiologic parameter, a microelectromechanical system, or an integrated electronic circuit.
As used herein, “active element” will hereinafter be referred to as “sensor”, but it should be understood that this invention shall not be interpreted in a limitative manner, and one of ordinary sill in the art will easily understand that it covers not only sensors as such, i.e., signal transducers that produce an electrical or optical signal that is function of the variations of a physical parameter, but also active electronic circuits such as amplifiers, filters, etc., whether or not associated to a sensor, in the vicinity thereof, or micro-electromechanical systems (MEMS), and more generally any element technologically integrable onto a substrate in a material such as silicon or any semiconductor material, consistent with the definition of active element.
Implanted sensors are subjected to very strict requirements, particularly when they are in direct contact with blood or other body fluids, and especially when said contact is very long or permanent, i.e., over a duration of several years in the case of cardiac implants.
These requirements are preferably as specified in the ISO 10993 series of international standards, and are of two kinds:                biocompatibility of the materials in use, that is to say that, on the one hand, these materials shall remain totally inert towards surrounding body tissues and fluids (harmless), and, on the other hand, these tissues or fluids shall not induce any corrosion or degradation of the material properties, which shall remain intact notwithstanding the prolonged contact with surrounding biological medium.        Hermeticity, that is to say that the sensor shall withstand not only the fluid ingress (tightness), but also ingress of gasses, which requires a perfectly controlled and minimized leak rate.        
Heretofore, it has been considered sufficient to enclose or coat the sensor in a biocompatible material. More recent standards, however, now require a dual level of protection, with not only a biocompatible coating, but also biocompatibility of the coated element. The purpose is to ensure proper protection in the case of indirect contact, for example, due to the diffusion through the coating, between the sensor and surrounding medium, or in the case of degradation, cracking, etc., of the coating after a prolonged period of time.
In order to comply with these very strict requirements, it is known to embed the sensor in an inert metal case, usually made of titanium. Ceramic feedthroughs welded on the case allow to establish electrical connections between the sensor enclosed inside the case and the outside, in order to establish the connection to the internal lead conductors.
This solution complies with the biocompatibility and hermeticity requirements noted above. However, such a solution is expensive, due to the technology that is not easy to implement, components that are costly and difficult to assemble, and the difficulty to implement for an automatic manufacturing process, and a fortiori collective processing, which would allow mass production. Moreover, this known technique leads to components having a relatively large volume because the case cannot be miniaturized as much as desired.
Also, there is an existing and increasing need for small sized sensors to be notably placed on very small diameter leads, which are compatible with common practice in terms of implantation through a venous network catheterization.